New to Dexcom

I have had T1D since I was 14. I have always had mostly good control (A1Cs in the six range) but have really tried to tighten control because I would like to get pregnant (A1C currently 5.8). So I decided to finally try a cgm and just put the Dexcom on yesterday.

I noticed yesterday major spikes after a meal. At dinner and today I tried doing the bolus then watching the dex. It takes about an hour for the downward arrow to appear. Then I eat. It has prevented a major spike.

But it just shocks me it takes that much time for the Humalog to start working. I remember all the times I ate first then took a shot (about 15 years ago some idot nurse told me it would be fine to do).

Has anyone else noticed this? Would be especially interested in hearing how other ladies dose insulin to stay in range during pregnancy.

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I have used Apidra, Humalog and Novolog. For me both Apidra and Novolog are much faster acting than Humalog.

Thanks! I have an appointment with my endo in a couple weeks. I will ask to switch.

Erica, that’s exactly how we do it (my 12-year-old is T1D). By doing that, and by staging meals (wait for a while after the end of the meal to take desert or to drink milk) we can get a very flat curve.

Most of the time, it takes about 25 minutes for my boy’s insulin to start being seen in the G5 (not the elbow, but the first slight drop). But it happens often that the downwards trend only starts 40-60 minutes after dosing. So, when he is not at school, we do exactly what you describe except when the meal is very low-carb. If he does not pre-bolus properly, he will definitely spike almost all the time.

Re the advice you got: we are figuring out now (after not quite a year at it) that the advice we are getting at the clinic is not for fine tuned diabetes management, but simple and approximate rules that are simple enough for anyone to understand. YDMV of course.

It was only after I got my Dexcom that I realized that Humalog could take 45 minutes to an hour to have visible action. The other thing to remember is that when you see the down arrow you are actually observing blood sugar readings from 15 minutes earlier.

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It’s so frustrating that doctors and nurses don’t have better information. Then again most probably don’t understand it themselves.

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That’s right. Hmm.

Erica, there are/have been several threads lately about pregnancy - if you do some searches you would be able to quickly identify several members who are pregnant right now or have been and gave birth recently. Here are some threads:
Baby is here
Labor naturally with T1D
Due date tips
First pregnancy A1C of 9
First time pregnancy
Pregnancy while honeymooning
Low carbs and diabetic prgenancy
Spikes in first weeks of pregnancy
Pregancy concerns
Pregnancy and crazy BGs
Pregnant and can’t keep my glucose down


Bolusing early is very helpful. But putting a time-range on it will never be exact, because it depends on so much! What your BG is, which way it is moving, how quickly it is moving, and also what you are eating.

To reduce the post-meal spike, try keeping track of those things, and make adjustments to how soon you bolus before the meal.

If it is not too sharp a drop, when your BG is just beginning to start moving into the low area, and you start eating, those two things can cancel out nicely, and your Dexcom will look like a non-diabetic is wearing it. It just takes practice and adjustment.

Keep in mind what Brian said, the Dexcom is a bit behind.

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Hi Erica,
I learned the same thing in 2007, when starting Minimed CGMS. I had been following ‘doctors orders’ of only testing 4x/day to figure out insulin dose. Never checked after a meal to see how high it was getting, and of course was following the conventional rule to eat within 15 minutes of dosing, using the recommended exchange diet (lots of carbs). However, having frustrations while using MM CGMS, I searched online, and that’s when I discovered this forum, so at least something good came out of it. In 2010 I switched to Dexcom CGMS.

You can look into the ‘sugar surfing’ techniques, and check below website for an idea of what that’s about. There is also a book with more details. There are other discussions on this forum related to that too if you search it. The author is Stephen Ponder, who is T1D endo.
sugar surfing

The Flatliners forum is also a good place to see how people analyze their CGMS data to make adjustments, and share their successes (and not so successful endeavers).

Erica, forgot to mention. Because they are faster for @Helmut does not mean they are faster for you. These are very individual things. But it might be worth testing to see - with a CGM you can do a lot of testing:-) For us, for instance, there is practically no difference between Humalog and Novolog.

Also, you might want to check which insulins are on your (insurance) formulary. Your insurance company may only cover some insulins.

Agreed. With the help of the dex it should be easy to figure out which one works best for you.

As suggested, best to find out first if covered by insurance. I have not tried Aprida since not covered. Humalog and Novolog are about the same for me, and my insurance switches between them, currently using Novolog. Also check with your doctor for samples. Then if you notice significant difference, you can do battle with ins if not preferred.

Exactly. In fact there are no reliable scientific studies that compare the three rapid analog insulins against each other. The only studies are those that compare each individually against regular human insulin. From these it is not possible to identify any statistically significant differences. That said there are suggestions from the data (and also some anecdotal evidence), that Apidra has a slightly quicker onset and a slightly shorter duration of action than Humalog and Novolog. The downside of Apidra is that in subset of people that are prone to site problems, Apidra can be more likely to do so than the other two. You will probably get the best results by first using your CGM to try to optimize dosing using your current insulin - if you want to then try a different analog, you will be better able to compare the differences.

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I was pretty shocked, when I started a Dex, about how differently the system behaved than how I imagined/was told that it behaved. Unfortunately, I really overreacted to those post meal spikes when I saw them coming through in real time via the Dex. Give yourself time to re-evaluate your numbers. Your perspective will change. Remember the rule: Check bg before you eat, check 2 hours after you eat. That’s how you adjust your meal bolus. Don’t over-react to what happens within that 2 hours period. Take time to understand the data and what can/cannot be controlled.

Ive been using dexcom for a year now. Stephens Ponder book “Sugar Surfing” provided some interesting insight and helped me understand some complex but great concepts for my data analysis, good advice @MM1 :slight_smile:

I think it varies with each person and with each drug. For our son, a prebolus does seem to help some, but we don’t have to wait a full hour. In the morning it could be up to 25 minutes but during the day it seems to cause a drop in 10 to 15. Also keep in mind that CGM is measuring interstitial fluid, which is up to 15 minutes behind blood glucose. So once you see the downward arrow on CGM, your blood sugar has likely been dropping for 10 minutes or more.

However, I think it is really important for people to realize that insulin activity actually peaks about an hour into your dose …that means, it’s maximum glucose-lowering effect occurs an hour after you inject. And it takes a full 30 minutes, just based on the graphs shown in the packet inserts for the drugs, for a meaningful level of insulin activity to be present.

Realizing this has led us to do a small pre-bolus about an hour before our son eats (typically about 0.3 units), and then bolus for the rest of his meal (usually 1 to 2 units) upfront. We’ve found that this type of prebolus works better for our son as he’s small and it actually takes him a few hours to digest food. If we prebolus for the entire amount upfront, his food outlasts his insulin and he gets a rise 2 to 3 hours after eating. My hunch is that the sharp spikes we saw before with no prebolus were caused by liver dumping in anticipation of eating, so the prebolus of 0.3 is just enough to suppress that dump, and that the actual metabolism of glucose from the food can be handled by the rest of the bolus given anywhere from 5 to 10 minutes before to 10 minutes after a meal.

The other benefit is that if he decides to throw a tantrum and chooses not eat his meal, we’ve bolused for so little that it’s very easy to stop any impending low with a few jelly beans. By contrasting, making up for a whole prebolused meal that he refuses to eat typically takes a lot of quick thinking and scrambling.

Then again, we are not aiming for very tight control; his endo target is 7.5, I aim for below 6.5. Using this I would say he routinely spikes to between 160 and 180 post-breakfast, 140 to 150 post lunch, and 150 post-dinner. Often it’s higher, of course.

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I used the Dexcom 7+ and then the G4 with the original software. With those systems, it was serious business when you got double-up or double-down arrows.

When the G4 system got the 505 algorithm software update (and the software that the G5 uses), I found that I got a lot more double up arrows than previously. I continued to respond aggressively every time I saw them and finally learned not to. There are times that I will be double-up arrows at BG 100 after eating. I get ready for a huge spike up to 200+. Then it levels out and peaks at 129. For me it didn’t work that way for the older Dex versions.

For me it has definitely been a learning process through my 5+ years of using Dexcom to understand how to react or not react to the information it gives me.

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